In recent years, attention has been paid to a silicon device which is fabricated by integrating on the same substrate various kinds of sensors used for measuring inertia force, a pressure, and other various physical quantities, which are induced by, e.g., acceleration or angular velocity, a fluid sensor having a flow channel provided on a silicon substrate, and a power device that handles a high voltage or a high current.
Such a sensor has, e.g., a cantilever beam or a hollow structural mass body fabricated on a silicon substrate by MEMS (Micro Electro Mechanical System) technology or a hollow structure fabricated in the silicon substrate. As an example of a method for fabricating such a sensor on a substrate, a method using an SOI substrate has been reported (Patent Literature 1). In Patent Literature 1, an SOI wafer having an insulator film on a base substrate and a thin-film layer on the insulator film is prepared, and a bridge resistive element serving as a sensor unit, a control unit (a CMOS circuit), and a wiring unit are fabricated on a thin-film layer surface of the SOI wafer. Then, a front side and a back side of the SOI wafer are covered with a protective material (a resist), a window is formed in a back side portion corresponding to the sensor unit by photolithography, and then a back side silicon portion corresponding to the sensor unit is formed into a thin film by etching. Then, this product is attached to a glass substrate, and a pressure sensor is brought to completion. Further, as a method for fabricating a high-voltage/high-current power device on a substrate, a method for separately arranging a portion to which a high voltage is applied and any other portion on respective device regions has been introduced (Patent Literature 2).